(1) Field of the Invention
The present invention relates to image coding methods, image decoding methods, image coding apparatuses, and image decoding apparatuses, and in particular to an image coding method, an image decoding method, an image coding apparatus, an image decoding apparatus, and an image coding and decoding apparatus intended to perform arithmetic coding or/and arithmetic decoding.
(2) Description of the Related Art
Recent years have seen an increase in the number of applications for services of, for example, video on demand type services. Examples of such services include video-conferencing through the Internet, digital video broadcasting, and streaming of video contents. These applications require that video data having a substantial amount of digital data is transmitted through transmission channels and is stored on storage media. However, conventional transmission channels have a limited available frequency bandwidth, and conventional storage media have a limited capacity. Accordingly, in order to transmit the video data using a conventional transmission channel and to record the video data onto a conventional recording medium, it is inevitable to compress or reduce the amount of the video data.
For the purpose of compressing video data, many video coding standards have been developed. Such video coding standards are, for instance, International Telecommunication Union Telecommunication Standardization Sector (ITU-T) standards denoted with H.26x and ISO/IEC standards denoted with MPEG-x. The most advanced video coding standards are currently the standards denoted as H.264/AVC or MPEG-4/AVC (see ISO/IEC 14496-10, “MPEG-4 Part 10 Advanced Video Coding”, and Thomas Wiegand et al, “Overview of the H.264/AVC Video Coding Standard”, IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY, JULY 2003, pp. 560-576).
The data compression processes in the H.264/AVC Standard is roughly divided into prediction, transform, quantization, and entropy coding. The entropy coding is intended to reduce redundant information in information to be used for the prediction and quantized information. Representatives of entropy coding include variable-length coding, adaptive coding, and fixed-length coding. Representatives of variable-length coding include Huffman coding, run-length coding, and arithmetic coding. Among these, the arithmetic coding is known as a scheme which is intended to determine output codes using contexts for identifying symbol occurrence probabilities and which provides a high coding efficiency by switching contexts according to the features of an image, compared to Huffman coding which uses a fixed coding table.